This invention relates to an apparatus for use during the production of multifilament, synthetic yarn. In particular, it relates to a muffler, for use in conjunction with an interfloor tube and aspirating means, which reduces by up to 33.5 .DELTA.dB(A) the noise emitted at the exit end of the interfloor tube when the aspirating means is operational.
Throughout the present specification and claims, the term "dB(A)" (decibels - A-weighted) connotes a unit of measurement of sound level corrected to the A-weighted scale, as defined in ANSI S1.4-1971, using a reference level of 20 micropascals (2 .times. 10.sup..sup.-5 Newtons per square meter). The term ".DELTA.dB(A)" refers to the difference between two noise levels where each level is expressed in units of dB(A). The term "yarn" is employed in a general sense to indicate strand material, either textile or otherwise, and including a continuous, often plied, strand composed of fibers, filaments, glass, metal, asbestos, paper, or plastic, or a noncontinuous strand such as staple, and the like. An "end" is one of a contiguous group of such strands of yarn.
The invention is applicable to many phases of yarn handling, the particular use disclosed herein being merely illustrative and not limiting thereof.
In a typical melt spinning process, one or more filaments is extruded from one or more spinnerettes and passed into a quenching chamber for cooling. Further process equipment, for instance drawing or winding apparatus, is usually spaced a considerable distance vertically downward therefrom. In fact, it is normal practice to have the process equipment spaced over three tiers with the extrusion apparatus occupying the uppermost tier or floor, the quenching apparatus occupying the intermediate floor, and any further process equipment residing on the bottom floor. In order to convey the yarn from the quenching area to the bottom floor, it is conventional to provide an interfloor tube. To initiate string-up, an operator cathces the advancing quenched filaments and throws them towards the entrance to the interfloor tube through which they fall to be picked up by either a string-up aspirator or a panel aspirator. Aspirating means is usually employed in conjunction with the interfloor tube for one of two reasons. First, it is often necessary to accelerate the speed of the yarn to extrusion speed as the yarn does not fall fast enough by itself due to drag. Second, the smaller the inner diameter of the interfloor tube is, the greater the necessity for aspirating means due to the drag on the yarn. Therefore, to initiate string-up, aspirating means for use in conjunction with the interfloor tube should be turned on and remain on until the yarn end or ends thrown therethrough have been picked up by either a panel aspirator or a string-up aspirator, at which time is turned off.
The aspirating means is located at the inlet portion of the interfloor tube where high velocity air is introduced and directly downwardly to create the desired suction effect. Noise is produced at and downstream of the point at which this high velocity air is introduced. The sound waves thus generated are then propagated primarily through the exit end of the interfloor tube. Noise issuing from the exit end impinges on the lower floor operator who picks up the yarn ends to continue string-up. The noise emitted, as measured 6 inches and 90.degree. from the center line of the interfloor tube exit end with an air supply line pressure of 90 psig, has been found to exceed 110 dB(A) in some instances without use of this invention. The frequency component of the interfloor tube noise is situated in the high frequency levels, i.e., greater than 2,000 cycles per second, which has been shown to be more harmful than the low frequency levels.
The high level noise from the interfloor tube occurs only during string-up, but as a minor component in a process which has several other sources of noise, it is desirable to bring its noise level down to tolerable limits. There are several approaches to noise reduction in a work environment. One is the use of hearing protection devices such as helmets, ear plugs, or each muffs by the operator exposed to the noise. The protection afforded, however, relates directly to proper use and maintenance of the devices. The difficulty, from a managerial viewpoint, lies in getting the operator to use these protective devices. To avoid this problem, applicants have provided a muffler which reduces the noise emitted at the exit end of the interior tube by up to 33.5 .DELTA.dB(A) and which thereby brings the noise to within acceptable levels.